1. Field of the Invention
The present invention relates to aluminum-copper-iron quasicrystal alloys and in particular abradable quasicrystal coatings that exhibit low-friction properties.
2. Description of the Related Art
Quasicrystals are materials whose structure cannot be understood within classic crystallographic methodology. These quasiperiodic structures have a long-range orientation order, but lack transitional periodicity. Conventional crystals consist of repeated copies of a single geometric atomic arrangement--a unit-cell stacked upon each other like bricks. Quasicrystals, on the other hand, while also being built up from a single type of atomic clusters, differ in that adjacent clusters overlap, sharing atoms with their neighbors. When clusters overlap by sharing atoms (quasiperiodic packing), they produce denser atomic arrays than conventional, periodic, repeated packing patterns.
The non-periodic structure of Quasicrystals yields a broad, previously unobtainable range of physical properties embodied within a single material. Quasicrystals exhibit poor thermal conductivity while remaining stable up to about 1100.degree. C. Thus, a thin layer on a heat-conducting surface will distribute heat evenly eliminating "hot spots". These hard coatings promote wear and scratch resistance. Furthermore, due to their low coefficient of friction and electronic structure (low surface energy), they possess non-adhesive properties. Finally, they offer resistance to both corrosion and oxidation.
Researchers have identified over eight hundred different quasicrystal alloys. Many of these alloys contain a combination of aluminum, copper and iron. The Al--Cu--Fe alloys yield the specific icosahedral quasicrystal identified in atomic percent as Al.sub.65 Cu.sub.20 Fe.sub.15. (Note: This specification expresses all composition in weight percent, unless specifically noted otherwise). Furthermore, in some instances these alloys contain additional alloying elements such as, chromium, cobalt and nickel. This enables the alloy to accommodate specific operating conditions. For example, DuBois et al., in U.S. Pat. No. 5,204,191, describe several Al--Cu--Fe alloys containing quasi-crystalline phases.
Regardless of chemistry however, quasicrystals do not lend themselves to conventional fabrication. They can not be formed or readily cast; however, they can be reduced to powder and thermally sprayed to form an adherent, useful coating. As far as known however, none of these alloys have established widespread commercial usage.
It is an object of this invention to produce an Al--Cu--Fe quasicrystal alloy coating having decreased hardness for improved abradability.
It is a further object of this invention to produce an abradable Al--Cu--Fe quasicrystal alloy coating having high temperature stability and oxidation resistance.